How do I delete the inserted image from a image field

[吕荣吕59031656]

For example:

in a form, insert a "Image Field".

save the form as pdf file.

open the pdf file in Adobe Reader, click the image field, select a image, click OK, then the image will be inserted into the form.

The problem is if I want to delete the inserted image, what can I do in Livecycle Designer??